Re: vacuum, performance, and MVCC

On Mon, 26 Jun 2006, Jan Wieck wrote:

> On 6/25/2006 10:12 PM, Bruce Momjian wrote:
>> When you are using the update chaining, you can't mark that index row as
>> dead because it actually points to more than one row on the page, some
>> are non-visible, some are visible.
>
> Back up the truck ... you mean in the current code base we have heap tuples 
> that are visible in index scans because of heap tuple chaining but without 
> index tuples pointing directly at them?

In current code, no. Every heap tuple has corresponding index tuples.

In Bruce's proposal, yes. You would have heap tuples without index tuples 
pointing directly at them. An index scan could only find them by following 
t_ctid chains.

Correct me if I understood you incorrectly, Bruce.

- Heikki